Antimony plating bath and process



2,823,176 ANTIMONY PLATING BATH AND PROCESS Elmer R. Breining, Warren, Cleveland'F. Nixon, Detroit, and William R. Vincent, Birmingham, Mich., assignors to General Motors Corporation, Detroit, Mich., acorporation of Delaware a No Drawing. Application November 30, 1953 Serial No. 395,292

8 Claims. (Cl. 20445) This invention relates to improvements in the electrodeposition of antimony and more particularly to an improved electrolyte for the deposition of smooth adherent coatings of antimony.

In many instances electrodeposits ofantimony produced by prior antimony plating solutions and processes have not only been coarse-grained, poorly adherent and extremely brittle but also have had a poor surface quality which has necessitated extensive bufiing and/ or polishing.

We have now discovered that an improved electrodeposit of antimony is obtained fromelectrolyt'es utilizing a combination of certain addition agents. The first type of addition agents of the present invention comprises sulfonated hydroxy aromatic compounds and preferably those which, in addition to a sulfonate radical and hydroxy grouping, have at least one additional substituted grouping which is capable of complexing dissolved metals jtoform five or six membered ring structures. Typical of the type of organic addition agents contemplated in the present invention are the compounds obtained by sulfonating substituted phenols, catechol, derivatives of catechol such as 3-5 dihydroxy toluene (orcinol), isomers of catechol such as resorcinol; trihydroxy phenols such as pyrogallol, phloroglucinol; hydroxy aromatic carboxylic acids such as salicylic acid or B-resorcyclic acid; hydroxy aromatic aldehydes such as salicylaldehyde; 8-hydroxy quinoline; and naphthols such as 1-3 or 1-8 dihydr'oxy naphthalene.

In certain applications, it is advantageous to'employ,'in addition to, or in lieu of the above-mentioned additives, certain unsulfonated compounds including p'olyhydric alcohols such as glycerol, ethylene glycol, propylene glycol,

mannitol, sorbitol, dulcitol, erythritol, or pentaerythritol;

unsulfonated sugars such as dextrose, levulose or sucrose;

as well as unsulfonated sugar acids such as gluconic mucic, and saccharic acids. It will be understood, of course, that the present invention contemplates the use of the above addition agents as well as mixtures thereof. Moreover, sodium, potassium, ammonium, amine, or antimony salts of the various compounds also may be used.

In general, additives of the present invention form various complex organo-metallic salts which regulate the availabilty of metallic ions in solution. The actual chemical and electrochemical reactions occurring during plating using the additives of the present invention are not clearly understood at present. However, the following discussion, indicating sulfonated catechol as an additive, is set forth to aid in understanding the invention.

Sulfonated catechols may be used effectively in either acid or alkaline antimony plating baths. It will be under-. stood, of course, that in the sulfonation of catechol, mono, di and tri sulfonic acids are obtained, the amounts of "ice in the following reactions, although a mono-sulfonic acid is illustrated, similar reactions occur usingdi-sulfonic acid, tri-sulfonic acid or a mixture of these acids.

The efiectiveness of the sulfonated catechol is thought 6 to depend primarily on the complexing of antimonious hy- Compound Formula Antimony Catechol CtHiOtSbOH Antimony Pyrogallol CrHtOa-S'DOH SCHZCOOH AntlmonylTbloglycolllc Acld..-. --eab 1 I l i r r isomc o oon. i g s-t'3-00011 AntimonylThiolacttc Acid sb P's-0410011. CH:

AntimonylThioglycollamlde.......... 7 Sb(SCHiG 0NHr)r Ethylene ilycoLun n, liege-on i i 4.;miotzi'ij each depending upon the technique ofsulfonation. Hence,

droxide which, in an acid solution, is indicated as follows:

The following reactions indicate the ensuing formation of mono-sulfonated antimony-catechol complex:

Sb-OH BF :1,- Sb-F 11.0 son; 0 SOaHOO (3) on o sbF. :2 SbF 2111 son: on son; 0

SbF axon 2* SM mo 503K 0 sonzo In an alkaline bath a similar series of equilibrium reactions occur as summarized in the following equation:

sb-o-K 3KF 411.0 soil: 0

It will be understood, of course, that analogous antimony complexes can be formed using other additives of the present invention. The following table summarizes by compound and corresponding formula some of the antimony complexes formed in accordance with the present invention.

- 2,823,176 v V r p F Compound Formula Metal Constituent Source of Metal Solubility C Al2(S04)a.9H2O Soluble.

BaFz Slight. Pr pylene Glycol sboH Very; Slight.

O. C linkage Slight.

Soluble Slight.

Do. Trimethylene Glycol sb -0H 113o. 2 o. (J "liri'kag'e' Do. Do. p D0.

Soluble. lycermen :sb-o:H. Very Slight.

Soluble. -C 'llnkage" Do. Do.

Erythfltol Sb0H The fol levying are examples of antim ny "baths in 1 cordance with the present invention as used in acid media in which-the'quantities'expressed are:per liter of water: Penta Erythritol I E p I 4c -g 125 g. antimony fluoride 135 cc. sulfonated catechol (81.0 g. catechol) 175 g. potassium hydroxide Sorbitol sb-OH 10 g; alumihu'mz-sulfate O linkage 0 pH .-1-4.0. Current"densit-y..;... v15425 A. S. F. Mannltol Sb=0H 0 Temperature; 115 125" F.

' hnka-ga 3 Anodes :Bagged antimony.

Agitation..-. Cathode rod. Arabltol I H il ixam'ple' II 220 g. 'a'ntu'n'o'ny fluoride v *0 'lmkage 241 cc. st'ilfonated catechol (144.5 'g. catechol) 0 50g. magnesium'sulfate .heptahyfdrate Dumml n 300 potassium hydroxide iliikjagv pH 3:2 i I Current densi 15-25 A. S.' F l r antimony complexes may be formed lISlBg poly- 40 Temperature ty r oa hydroxy aldehydes and ketones-,;polyhy.dric alcoholsiof the 'Anodes l T B g antimony cycl-ohexane type such as quercitol and inositol, as well Agitation Ca h d das various sugar acids.

In general, organic antimony complexes formed in ac- Example cordance with'the-present invention may be characterized 220 go afltlm'ofly fluoride as organic esters and/orvthioesters having the following structure:

The second type ofadditive',wbicli maybe iised'rloii' preferably are provideclby the additionto-therplating solution of water s oluble :salts of the desired metals such as sulfates, nitrates, acetates or chlorides although satisfactory resultsalsoi 'a're obtained by employing salts which are relatively orzs'ubstantially insoluble,inavater rsuflicient dissolution being obtained in the plating solution. The following tabulation :sets forth a number of inorganic eations whichlmay be employed in thepra'etice of "the presena-invention.

241 cc. sulfonated catechol'i'(.l44.5 g. catechol) 325 g. potassium.:hydroxide 50 g. zirconiumfluoride Current density 20 A18. F.

Temperature 130 F.

Anodes Bagged antimony.

Agitation Cathode rod.

Example? IV 220 --;g; antimony fluoride 235 cc..sulfona ted c'atechdl (141.0 300 g. potassium hydroxide 25 g. nickelwcatechol sulfonate g. catechol) 220 antimony fluoride V 235 cc. sulfon'atedzcatechol (141.0 gi catechol) 300 .g. -potassium-.;hydronide 7 Agitime;-TI:IIIIIIIIII. Ca'th'o'de'rod.

' square foot.

The above baths may be operated satisfactorily within a pH range from about 1 to 5, the upper pH limit generally being that at which precipitation of antimony occurs. It is preferred to operate the bath using a current density within the range of from to 25 amperes per The preferred bath temperature is 120 F. although the baths generally may be operated at a temperature Within the range from room temperature, i. e., 70 F. to 75 F., to about 165 F.

In many instances it is preferred to employ a metallic salt of an organic additive such for example, as nickel catechol sulfonate or cobalt catechol sulfonate. Such a salt provides additional organic additive in solution while supplying the desired inorganic cation without introducing undesired foreign ions into the bath.

Acid baths of the present invention as illustrated by the foregoing examples generally may contain from about 20 to 300 grams per liter of dissolved antimony, 150 grams per liter being preferred and about 20 to 300 grams per liter of total organic additive. Using antimony fluoride, 110 to 265 grams per liter produce superior results, 220 grams per liter being preferred. The amount of potassium hydroxide to be employed is determined by the amount of free acid present in the organic additive, the concentration of antimony, and, of course, the pH desired. The quantity of a particular metal salt (source of the cationic additive) to be used generally may vary from a small but effective amount, i. e. a few milligrams of metal per liter, to an upper limit determined by the solubility of the salt in the plating solution.

Illustrative of an alkaline bath embodying the invention is the following in which the quantities expressed are per liter of water:

Example VI 90 g. antimony fluoride 150 g. potassium hydroxide 95 cc. catechol sulfonate (57 g. catechol) 10 g. aluminum sulfate Current density 24 A. S. F. Temperature 120 F.

Anodes Bagged antimony. Agitation Cathode rod.

Alkaline plating solutions embodying the present invention may be operated at various pH values although it is preferred to employ a pH of 10 or higher, the upper practical limit or pH being that at which undesirable precipitates form. The amounts of the alkaline bath ingredients can, of course, be varied, the organic additive content varying from about to 390 grams per liter. The maximum antimony content is generally dictated by the solubility of the antimony compound in the bath, the amount increasing with an increase in pH. To employ a maximum amount of antimony, it is essential that the molar ratio of antimony to the organic additive be at least 1:1. The amount of potassium hydroxide depends on the pH regulation necessary. As in the case of acid baths, the quantity of inorganic ions utilized may vary from a very small amount, such as a few milligrams of metal per liter up to the limit of solubility of the source of the cations in the plating solution.

Various antimony salts, in addition to antimony fluoride, such as antimony oxide, antimony sulfonate, antimony pentafluoride, antimony pentoxide, potassium meta antimonite, butyl amine antimonyl tartrate, urea antimonyl tartrate, aniline antimonyl tartrate, benzyl amine antimonyl tartrate, phenyl hydrazine antimonyl tartrate, ammonium antimonyl citrate, potassium antimonyl glycollate, potassium antimonyl citrate, sodium antimonyl citrate, antimony potassium tartrate, antimony sodium tartrate, and antimony tartrate also may be employed.

Similarly, instead of the sodium hydroxide or potassium hydroxide indicated in the examples, the pH may be regulated using ammonia, or organic amines, such as I butyl amine, trimethylamine or ethanolamine.

5 In the electrodeposition of antimony, as in other plating processes, proper preparation of the surface to be coated is essential. In depositing antimony on copper, for example, we have found that it is desirable to electrolytically etch the surface to be coated for about one to five minutes at a current density of approximately 5 amperes per square foot in a 63% by volume solution of phosphoric acid. In depositing antimony on steel it is generally advantageous to etch the steel in nitric acid, preferably diluted 1:3.

As an example of the preparation of a plating bath embodying the invention, 890 grams of catechol were added slowly to 1568 grams of C. P. sulfuric acid while maintaining the temperature of the reaction mass within the range from 85 C. to 95 C. for two hours after the last catechol was added. The resultant catechol sulfonic acid contained approximately .62 gram of catechol per cubic centimeter of crude sulfonation mass. To complete preparation of the bath, 241 cc. of the sulfonation mass was then added to an antimony fluoride solution containing about 165 grams per liter of antimony, and 50 grams per liter of aluminum sulfate, the pH being adjusted to about 5 using sodium hydroxide.

It is to be understood that, although the invention has been described with specific reference to particular embodiments thereof, it is not to be so limited since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

What is claimed is:

1. An electroplating bath comprising approximately 20 to 300 grams per liter of solution of antimony, a metallic cation in addition to antimony in a small amount effective to provide a smooth, adherent, non-brittle antimony plate up to the maximum amount soluble in the plating bath, and a complexing agent capable of complexing dissolved antimony to form a five-membered ring, wherein said ring-forming complexing agent is sulfonated catechol present in approximately 20 .to 300 grams per liter of solution.

2. An electroplating bath as in claim 1 in which the metallic cation other than antimony is aluminum.

3. An electroplating bath as in claim 1 in which the metallic cation other than antimony is zirconium.

4. An electroplating bath as in claim 1 in which the metallic cation other than antimony is magnesium.

5. An electroplating bath as in claim 1 in which the metallic cation other'than antimony is nickel.

6. An electroplating bath as in claim 1 in which the metallic cation other than antimony is copper.

7. An electroplating process which comprises passing electric current from an anode to a cathode through the bath of claim 1.

8. An electroplating bath as in claim 1 in which the 60 antimony is present in the form of antimony fluoride.

References Cited in the file of this patent UNITED STATES PATENTS 2,461,350 Schaefer et al Feb. 8, 1949 FOREIGN PATENTS 130,302 Great Britain July 29, 1919 OTHER REFERENCES Monthly Review American Electroplaters Society, vol. 29 (1942), page 870.

Soderberg et al., Plating, vol. 37 (1950), pp. 254-259. 

1. AN ELECTROPLATING BATH COMPRISING APPROXIMATELY 20 TO 300 GRAMS PER LITER OF SOLUTION OF ANTIMONY, A METALLIC CATION IN ADDITION TO ANTIMONY IN A SMALL AMOUNT EFFECTIVE TO PROVIDE A SMOOTH, ADHERENT, NON-BRITTLE ANTIMONY PLATE UP TO THE MAXIMUM AMOUNTSOLUBLE IN THE PLATING BATH, AND A COMPLEXING AGENT CAPABLE OF COMPLEXING DISSOLVED ANTIMONY TO FORM A FIVE-MEMBERED RING, WHEREIN SAID RING-FORMING COMPLETXING AGENT IS SULFONATED CATECHOL PRESENT IN APPROXIMATELY 20 TO 300 GRAMS PER LITER OF SOLUTION. 